1. Technical Field
The present invention relates to a piezoelectric oscillator used as devices such as a frequency control device, particularly to a storage case suitable for the highly stable piezoelectric oscillator that can output a highly stable frequencies, a heat source unit, an highly stable piezoelectric oscillator and a manufacturing method of the highly stable piezoelectric oscillator.
2. Related Art
Oven-controlled crystal oscillators are commonly known as piezoelectric oscillators, such as crystal oscillators, used as frequency control devices for mobile communication apparatus or transmittal communication apparatus. These oscillators output highly stable frequencies without being effected by external temperature change. In recent years, these highly stable piezoelectric oscillators are required to be smaller and lighter, corresponding to the needs of the market in the above field for various apparatuses to be smaller and lighter
For instance, an oven-controlled piezoelectric oscillator is disclosed in JP-A-1-195706. In this oscillator, a first substrate and a second substrate are combined. The first substrate includes an element for oscillator circuits arranged on both sides of the oven that contains a crystal resonator having a hot wire therearound, and the second substrate having an oscillation transistor arranged thereon. At the same time, the substrates are stored in a thermal insulation holder that has a body and a cover that fits an oscillator cover.
However, the piezoelectric oscillator disclosed in JP-A-1-195706 has a two-floor structure in which the two substrates are aligned in the height direction. This involves a problem of the height (thickness) increase of the piezoelectric oscillator.
A crystal oscillator made in consideration of the above problem is disclosed, for instance, in JP-A-2002-223122.
FIG. 8 is a sectional view showing a structure of a crystal oscillator disclosed in JP-A-2002-223122.
A crystal oscillator 100 shown in FIG. 8 includes a crystal resonator 103 and other elements 104 mounted on one print circuit board 102 to which terminals 101 are coupled. Moreover, a power transistor 105 is mounted on the print circuit board 102, and a crystal resonator 103 abuts this power transistor 105.
The crystal oscillator 100 shown in FIG. 8 requires a heat resistance between a metal case 103a of the crystal resonator 103 and the power transistor 105 to be minimum, in the arrangement where the power transistor 105 abuts the metal case 103a of the crystal resonator 103. One way of minimizing the heat resistance is to directly solder the power transistor 105 to the metal case 103a of the crystal resonator 103.
Direct soldering of the power transistor 105 to the metal case 103a of the crystal resonator 103 results in a thermal damage of the crystal resonator 103s. Consequently, this involves a problem of frequency deviation in the crystal oscillator, degrading the long-term stability thereof. In particular, an increasing requirement of recent years for smaller highly stable crystal oscillators, promoted a development of highly stable piezoelectric oscillators that use small crystal resonators. Such small content crystal resonators have had an inherent problem of frequency deviation caused by thermal damage, while it has not in large content crystal resonators.
The crystal oscillator disclosed in JP-A-2002-223122 can be formed thinner than the one disclosed in JP-A-1-195706, since it is formed with a single substrate, and does not have a two-floor structure. Unfortunately, the oscillator cannot be made any thinner, since the power transistor 105 is arranged so as to abut the crystal resonator 103 on the print circuit board 102.